[70RAlll]

Originally Posted by Bentwheelbob

Bruce,

Thanks again. I think this is right....

Now what vacuum source is "correct" to connect to the other nipple on the air inlet switch? Is it the fitting in the manifold front, driver's side? That seems like a long run from the rear of the air cleaner. Also, what is the conventional wisdom between yellow stripe vacuum hose vs. white stripe? Did the factory use both?

everything in this post appears correct to me. Vacuum to one side of the thermo valve, the other port supply's that vacuum to both snorkels when heated up.. I say it is exactly as you have it routed in these pictures.

[blue71ta]

Bob,
you actually had it right the first time. Here's a pic of my original 455 HO RA air cleaner with the original, white-striped hoses. The short one that comes off the tee in the front is the one that goes down to connect to the vacuum source on the intake manifold (the fitting that you have circled in your engine pic).

[Bentwheelbob]

Originally Posted by blue71ta

Bob,
you actually had it right the first time. Here's a pic of my original 455 HO RA air cleaner with the original, white-striped hoses. The short one that comes off the tee in the front is the one that goes down to connect to the vacuum source on the intake manifold (the fitting that you have circled in your engine pic).

If you plumb the vacuum lines like that, and like the black car was plumbed, one of the vacuum actuators will be closed at all times when the engine is running. These vacuum actuators are normally open, and close when vacuum is applied. That means that as soon as manifold vacuum is generated the actuator on the vacuum source side of the air inlet thermal vacuum sensor will close the flapper and as long as vacuum is present the flapper will remain closed and prevent fresh air from entering the engine. Also, the only way to get both vacuml actuators to work in unison is to have them both plumbed to the same side of the air inlet thermal vacuum sensor.

I need to do some more experimentation in the morning, but I think the air inlet sensor is normally open which lets the vacuum go through the "switch" so to speak thereby closing the flappers in both snorkles. Once the vehicle comes to operating temperature, the switch (air inlet sensor) closes thereby preventing the vacuum from passing through it and to the actuators. In the absence of vacuum, the flapper doors open and fresh air enters the combustion process.

This sounds good on paper and i think I am right.

[Pepi]

Originally Posted by Bentwheelbob

If you plumb the vacuum lines like that, and like the black car was plumbed, one of the vacuum actuators will be closed at all times when the engine is running.

That is what I was thinking.

[Bentwheelbob]

It sounds good on paper and I am completely wrong....

So after coming down from my post turkey and sweet potato high, and getting a good nights sleep., I broke out the heat gun and vacuum pump this morning. I was correct that the air inlet thermal vacuum sensor is normally closed, but both nipples on the bottom of the sensor are on the closed side. Pull a vacuum on one nipple of the sensor and it moves through the sensor and creates a vacuum on the other nipple as well. Put heat on the sensor and the sensor opens up on the top side of the sensor (that part on the interior of the air cleaner) and releases the vacuum. Once the vacuum releases it lets the flapper doors open. Those who said that the correct plumbing was as pictured below were correct.
I think...

BTW - the vacuum actuators on this air cleaner work perfect and hold vacuum, but show no sign of having been replaced unless NJSteve did his usual fine job.

[Pepi]

Originally Posted by Bentwheelbob

the air inlet thermal vacuum sensor is normally closed, but both nipples on the bottom of the sensor are on the closed side. Pull a vacuum on one nipple of the sensor and it moves through the sensor and creates a vacuum on the other nipple as well. Put heat on the sensor and the sensor opens up on the top side of the sensor (that part on the interior of the air cleaner) and releases the vacuum. Once the vacuum releases it lets the flapper doors open.

So once it opens up, and lets the vacuum out, it is a controlled vacuum leak... Got it now. Never checked mine, I always thought it allowed vacuum when cold and closed when warmed up stopping vacuum to the actuator.

Still trying to locate where I found the colored hose information.

[Judge273]

Mine is as blue71ta shows, and was routed plus checked per Brews 72 silver HO verified by Dan Jensen at TA Nats.

This will be a good tread all by itself.

[blue71ta]

Originally Posted by Pepi

So once it opens up, and lets the vacuum out, it is a controlled vacuum leak... Got it now. Never checked mine, I always thought it allowed vacuum when cold and closed when warmed up stopping vacuum to the actuator.

Still trying to locate where I found the colored hose information.

You are correct. When it is cold (with the engine turned off), the doors are closed on the bottom side. When you start the engine, the vacuum causes them to open, which allows the pre-heated air to come in from the ducting. Once the engine is fully warmed up, the vacuum is cut off, thereby closing the flaps again and allowing only the cool, outside air to come in through the hood vents / rubber RA boots (on the top side).

The system is designed to aid in cold startup / engine warm-up. Most factory GM air cleaners use the same system, but would only have one vacuum pod on a single snorkel air cleaner...

[Pepi]

Originally Posted by blue71ta

You are correct. When it is cold (with the engine turned off), the doors are closed on the bottom side. When you start the engine, the vacuum causes them to open, which allows the pre-heated air to come in from the ducting. Once the engine is fully warmed up, the vacuum is cut off, thereby closing the flaps again and allowing only the cool, outside air to come in through the hood vents / rubber RA boots (on the top side).

The system is designed to aid in cold startup / engine warm-up. Most factory GM air cleaners use the same system, but would only have one vacuum pod on a single snorkel air cleaner...

I knew they closed upon startup to allow the heat to help warm up the engine, just never knew the sensor "leaked" vacuum to allow them to open back up. That just seems strange to have a vacuum leak like that right off the manifold, instead of a ported vacuum switch.

[blue71ta]

yes, that is correct the way you have it now.
As an aside, the '71 and '72 T/A air cleaners have the vacuum lines routed the same way (with the 455 HO).